The present invention relates to video communications system for transferring image data sent in a G3-compatible fax transmission mode to fax machines connected to the Internet. Such G3-mode video data are transmitted with encoding techniques, for example, modified Huffman (abbreviated to MH hereinafter) encoding, modified READ (Relative Element Address Designate) (abbreviated to MR hereinafter) encoding, modified-modified READ (abbreviated to MMR hereinafter) encoding, and joint bi-level image experts group (abbreviated to JBIG hereinafter) encoding.
The G-interface standards is the standards for facsimiles, decided in G-series recommendation made by ITU-T (International Telecommunication Union-Telecommunication Standardization Sector/former CCITT). This fax standards is used for fax communications via regular telephone lines. The G-interface standards offers several transmission modes such as G1, G2 and G3 modes depending on image-transmission time. The most popular at present is the G3 mode using code-redundancy compression, bandwidth compression etc. Image-data encoding techniques available for G3 mode are HM, MR, MMR, JBIG, etc., listed above.
The MH encoding is one of compression encoding techniques for facsimiles in which image data is processed per scanning line using distribution information such as “A specific number of black exist”. The MR encoding is also called a border-difference sequential encoding technique, superior to the MH encoding on compression ratio. It is a two-dimensional encoding technique using correlation between scanning lines in the vertical direction, which may be correspond to an enhanced one-dimensional encoding technique. The READ encoding is a combination of RAC (Relative Address Coding) and EDIC (Edge Difference Coding) using their advantages. The JBIG encoding is the international standards for still-picture encoding techniques in which users can retrieve desired images from an image database and display them on monitor screen. This encoding technique achieves so called hierarchical transmission in which grainy images are transferred first, followed by gradually clean images, using the Markov encoding technique.
Internet fax machines have also been proposed in accordance with recent rapid development of computers. This type of machine is capable of transmitting image data via the Internet to a computer so that the data can be displayed on the computer screen or printed out by a printer connected to the computer. One of the standard image-file formats for Internet fax machines is TIFF (Tag Image File Format) in which the attribute of image data is defined for example with a tag information. This TIFF format allows data-type identification with a several-hundred-byte standard tag information stated in the head of an image file. Several types of flags for different image-data types are available for the tag information.
A known Internet fax machine is explained with reference FIGS. 9 and 10. Shown in FIG. 9 is a basic block diagram of the known Internet fax machine. The Internet fax machine is equipped with a G3-code data supplier 1A for supplying G3-compatible fax image data, an EOL detector 7 for detecting an EOL that indicates a segment between lines in code data, one-dimensional Huffman-code detector 8 and a two-dimensional code detector 9 for detecting one- and two-dimensional codes, respectively, a Huffman table 12 for storing Huffman codes, a decoded-data generator 14 for generating decoded data based on the outputs of the one- and the two-dimensional code detectors 8 and 9, a line memory 15 for storing the decoded data per line, a page memory 16 for storing the decoded data per page, a Huffman encoder 17 for generating code data corresponding to a code mode used for an internal Internet terminal, and a TIFF converter 18 for adding TIFF code such as a header for Internet facsimile to the generated code data.
The operation of the known Internet fax machine in FIG. 9 is explained with reference to the flowchart shown in FIG. 10. A decoding mode is detected in step ST1 and G3-compatible fax image data is received instep ST2. A start EOL is detected by the EOL detector 7 (step ST4), and it is determined whether the EOL has been found (step ST5). If found, the Huffman table 12 is looked up (step ST6), and it is determined whether there is a match on codes between the received fax image data and the Huffman table 12 (step ST7). If there is a match, decoded data is generated (step ST8) and the next data is requested (step ST9). It is determined instep ST10 whether a page-end code has been found. If found, the decoded page data is stored in the page memory 16.
The decoded page data is retrieved from the page memory 16 (step ST11) and sent to the Huffman encoder 17 for generation of Huffman code data for Internet facsimile (step ST12). Lastly, a TIFF header such as a header used in the Internet is added to the Huffman code data (step ST13). On the contrary, the procedure is brought to an error halt (step ST14) if no EOL has been found in step ST5 or no code has been found on the Huffman table, that should match the fax image data received in step ST7. Moreover, if no page-end code has been found in step ST10, the steps from ST6 to ST10 are repeated until a page-end code is found.
Transfer of image data received in a G3-compatible fax mode such as the above several types of encoding modes to another terminal via Internet facsimile requires decoding of the received image data such as MR-code image data to generate decoded image data and then re-encoding of the decoded image data into TIFF image data for Internet facsimile. This data transfer technique gives a heavy load to an image communications system for transferring imaged data received via a regular telephone line, etc., to another terminal in the communications system.
Moreover, most image data received in a G3-compatible fax mode such as MH-code mode and MR-code mode carry fill bits per line. The fill bits are stuff bits for indicating image data on one line as one-line data if the data on one line is less than the minimum line-transfer data amount for a constant one-line image-data transmission time beyond a specific time. The one-line image-data transmission time is for example about 2 seconds minimum. A standard fill-bit stuffing capacity corresponds to 5 seconds maximum.
Such fill bits are usually deleted from data for Internet facsimile when coded image data received via a regular telephone line is decoded and then re-encoded as Internet-fax data. However, if the image data is used as another type of fax data, the fill bits have to be reconverted even though they are unnecessary data for Internet-fax data.
Moreover, there is a situation in which a G3-compatible fax mode, for transferring image data to Internet facsimile which has been encoded in a specific encoding technique and transmitted from a usual facsimile, corresponds to image-data format handled by Internet facsimile. A header data such as a tag is then added to the image data received in the G3-compatible fax mode to form a TIFF-format data to be transmitted to another terminal, for such situation. This also requires transfer of fill bits unnecessary for Internet-fax image data in an image communications system. Such fill-bit transfer causes low transfer efficiency due to transfer of data unnecessary for skipping overhead or unnecessary procedures such as decoding/encoding in the same mode.